1. Field of the Invention
This invention relates in general to parachutes and more specifically to cruciform or cross parachutes. The present invention is a modification of the conventional cruciform parachute design, in which the arms are connected to form a parachute canopy configuration which is substantially square at the top and round at the lower edge.
2. Description of the Prior Art
Generally speaking, there are three types of parachute designs for personnel and cargo which are deployed from airborne aircraft. First, there is the conventional generally hemispherical canopy with the suspension or rigging lines connected around a continuous circular lower edge of the canopy. Second is the ram air type parachute with upper and lower surfaces generally in the shape of an airfoil with the suspension lines connected to the bottom surface. And, finally, there is the cruciform or cross parachute in which the canopy includes a generally square crown or center section with four wings or arms attached to the four sides with the suspension or rigging lines attached along the outer edges of the arms.
Because of their simple geometric configuration, parachutes having a cruciform or cross design are notable for their simplicity in construction and therefore low cost. Examples of modern cruciform or cross parachutes are shown in the prior art, such as in U.S. Pat. Nos. 3,331,573, 3,531,067, 3,559,931, 3,741,505 and 4,834,323. A major drawback of the cruciform parachute configuration, however, is the relatively large pendulum oscillation about the vertical, on the order 10xc2x0 to 15xc2x0, and other stability problems associated with this design. Efforts to overcome the oscillation and instability problems of cruciform parachutes have focused on extending the length of the arms to a length substantially greater than their width and to extending the length of the suspension lines. While these changes increase the stability and the drag coefficient of cruciform parachutes, they introduce new drawbacks, such as excess weight, bulk and costs, and the longer time constant of pendulum motion once initiated.
Furthermore, the rate of decent of a parachute can be decreased by using cloth for the canopy which has zero, or near zero, porosity. Such low porosity materials have been used in parachute design, especially in parachutes of the ram air type. However, as the porosity/permeability of the canopy fabric is decreased, stability is also decreased, and other problems such as opening shock are encountered. Thus, it has not been previously possible to utilize zero or near zero porosity materials in cruciform parachutes because the use of such materials increases the already unacceptable instability and oscillation of cruciform parachute designs.
The cruciform parachute designs of U.S. Pat. No. 5,839,695 (the xe2x80x9c""695 patentxe2x80x9d) seek to overcome the heretofore known problems in cruciform parachutes by providing air venting or air flow jets through appropriate vents or openings placed at selected locations in the wing or arm portions of the parachute canopy. By providing the air venting jets, zero, or near zero, porosity material can be utilized for the canopy of a cruciform parachute. The air venting or air flow jets of the ""695 patent are hereinafter referred to as xe2x80x9carm air flow jetsxe2x80x9d, or more simply xe2x80x9carm air jetsxe2x80x9d. The arm air flow jets of the ""695 patent are formed by generally horizontal elongated openings located in each of the four wings or arms of the canopy near where a tangent line which intersects the canopy surface forming the arms approaches a 45xc2x0 angle with the vertical axis of the parachute. This transition point is normally 15% to 30% of the arm length from where the arm is attached to the crown. Further, the arm air venting jet openings are preferably positioned centrally with respect to the width of the canopy arms.
However, the parachute design of the ""695 patent does not overcome all of the problems associated with cruciform parachutes. For example, cruciform parachutes can sometimes be difficult to pack because of the four separate arms extending in different directions from the generally square crown or central section. Further, there is the problem of reliability in packing in the event one of the arms is accidentally inverted.
Other prior U.S. patents which disclose parachute configurations that may have relevance to the present invention are U.S. Pat. Nos. 1,757,247, 1,834,370, 2,745,615, 2,942,817, and 5,472,394. It is also known in cruciform parachutes that the arms have been connected to each other through tapes, lines, or ropes in order to limit the excursions of the arms relative to each other, and to prevent them from inflating inside out if inverted.
However, in such circumstances, the adjacent edges of the arms are not attached to each other so as to form a three-dimensional shape that is substantially square at the top and round at the hem or lower edge. Further, cruciform parachutes have been built in the past using multiple pieces of material tied together, which in essence leave slits in the middle of each arm. These slits are running co-axially with the suspension lines, but their purpose is not to provide venting, and are not used in combination with arms attached to each other along adjacent edges.
The primary purpose of the present invention is to overcome the problems associated with known cruciform or cross parachutes, including the cruciform parachute of the ""695 patent. The improved cruciform parachute of the present invention is also made of zero, or near zero, porosity material and overcomes the stability and oscillation problems that previously plagued the cruciform parachute design.
In accordance with the present invention, a parachute of the cruciform or cross design, using zero or near zero, porosity material is modified by having the adjacent edges of the arms or wings of the parachute attached to each other while leaving generally vertical openings or vents between adjacent arm edges through which air can flow out from underneath the canopy. These openings or vents allow the higher pressure air inside the parachute canopy to escape. It has been surprisingly found that by connecting the arms together, an entirely new cruciform parachute design is created which forms a three dimensional shape upon inflation that is substantially square at the top and substantially round or circular at the hem or lower edge.
Further, it has been found in accordance with the present invention that the air jets necessary for a cruciform or cross parachute of zero, or near zero, porosity material can be formed at the connection of the arms where their adjacent edges are attached, and not preferably in the central portions of the arms as in the ""695 patent. Hence, in accordance with the present invention, air flow jets are formed below each corner of the generally square crown of the parachute. For the purpose of this invention, these air flow jets are referred to as xe2x80x9ccorner air flow jetsxe2x80x9d, or more simply, xe2x80x9ccorner air jetsxe2x80x9d. Also, in accordance with the present invention, the corner air jets can be formed by one or more generally vertical openings.
In addition, this new cruciform parachute configuration has the advantage of a continuous hem at the lower edge of the canopy. This continuous hem eases packing of the cruciform parachute configuration and improves reliability since accidentally inverting the arms during packing becomes impossible.
The size of the generally square crown or central portion of the canopy, the length of the lateral arms and the length of the suspension lines are designed so as to provide the desired stability and rate of decent using the zero, or near zero, porosity material whether for personnel or cargo use of the parachute. Shorter arm length and shorter suspension lines length than in conventional prior cross parachute designs can also be used in the present invention, without sacrificing stability, thus reducing the bulk and cost of the parachute.
In one embodiment of the present invention, the arms of the cruciform parachute are attached along their adjacent edges at vertically spaced locations to create a series of generally vertical openings at the four corners of the canopy. This series of vertical openings allows the high pressure air from underneath the canopy to escape. The forming of such corner air jets at the interconnection of adjacent edges of the arms of the parachute reduces the number and/or size of the generally horizontal arm air jets as described in the ""695 patent.
In a second embodiment, the bottom portion of the interconnected arm edges is attached continuously for a specified length of the side edges, leaving a single large opening or corner air jet between the upper side edges at each of the four corners of the canopy. In this embodiment, a majority of the side edges are left unattached, preferably, in the range of 60% to 85%. A single arm air jet can be included.
In a third embodiment, the arm edges are interconnected in a manner similar to the second embodiment, with a single large opening or corner air jet between the upper side edges at each of the four corners of the canopy, but the arm air jets are eliminated. In this embodiment, sufficient venting is obtained from the large openings, or corner air jets, to eliminate the need for additional venting from any arm air jets. This significantly simplifies the construction even further since the only addition to the conventional cruciform parachute construction is the interconnection of the arm edges for a specified length of the side edges from the hem or outer edges of the arms. There is no need for attaching additional reinforcing tapes, such as necessary for the arm air jets of the ""695 patent, because the side edges of the arms already have reinforcing tapes. It is therefore only necessary to attach the edges along their reinforcing tapes.
It is therefore an object of the present invention to provide a parachute of the cruciform or cross configuration type in which adjacent edges of the arms of the parachute are attached to each other while leaving generally vertical openings or vents through which air can flow out from underneath the canopy.
It is a further object of the present invention to provide a cruciform or cross configuration parachute in accordance with the preceding object which has a continuous hem or lower edge.
It is yet a further object of the present invention to provide a cruciform or cross configuration parachute in accordance with the preceding objects which has a new three dimensional shape that is substantially square at the top and substantially round at the lower edge or hem.
It is another object of the present invention to provide a cruciform parachute made from zero or near zero porosity fabric which has increased stability and reduced oscillation by providing corner air flow jets or openings in the connection between the adjacent side edges of the arms or wings of the canopy.
It is a still further object of the present invention to provide a cruciform parachute which can be more easily packed and with improved reliability because accidentally inverting the arms during packing becomes impossible.
It is yet another object of the present invention to provide a cruciform parachute wherein canopy sizes of from twenty up to sixty feet in diameter, when fully deployed, are capable of usage for air delivery of personnel.
It is a further object of the present invention to provide a cruciform parachute wherein canopy sizes of from 6 inches up to 15 feet in diameter are capable of usage for the air delivery of non-personnel payloads such as weapons and detection devices such as antitank mines and the like.
It is a still further object of the present invention to provide a cruciform parachute wherein usage with air delivery craft having higher air speed is possible without decreasing the stability of the delivery parachute.
Further still, it is another object of the present invention to provide cruciform parachute configurations which can be manufactured at lower cost with lower bulk, by reducing the arm and suspension line length in relation to the crown or center section.
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.